Mobile radio terminal and its moving speed detecting method

ABSTRACT

A moving speed detecting method of a mobile radio terminal which makes communication with a base station outputting a pilot signal includes a step of predicting phases and amplitudes of the pilot signal from the base station by using a plurality of prediction methods having different characteristics. A calculating step calculates errors for the prediction results, which are obtained for respective prediction methods in the prediction step, and a prediction error comparing step compares the prediction errors with respect to each of the prediction methods, which are calculated by the calculating step, to detect a moving speed of the mobile radio terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-333969, filed Oct.31, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a mobile radio terminal and itsmoving speed detecting method.

[0004] 2. Description of the Related Art

[0005] In a mobile communication system to transmit a pilot signal froma base station, as a method to detect a moving speed of a mobile radioterminal, the methods such as (1) a method to estimate a speed bydetecting a pitch of fading, (2) a method to estimate a speed from atime difference between a transmission frame and a reception frame, (3)a method to estimate a speed from a movement on a time axis by detectinga Path in a CDMA system and (4) a method to estimate a speed from thedisplacement of a career frequency by detecting a Path in a CDMA systemhave been already known.

[0006] The above described methods for detecting a moving speed of amobile radio terminal had the following problems, respectively.

[0007] (1) A conventional art to estimate a speed by detecting a pitchof fading requires a lot of complicated calculations to detect a pitchand it takes much time to average the obtained pitch.

[0008] (2) According to a conventional art to estimate a speed from atime difference between a transmission frame and a reception frame, adistance between a mobile radio terminal and a base terminal is detectedonce to estimate a speed as its time differential. However, the distanceis detected in units of 1 Chip (about 80 m in W-CDMA), so that it is notpossible to detect the speed for a movement of a terminal that isshorter than the length of 1 Chip.

[0009] (3) A conventional art to estimate a speed from a movement on atime axis by detecting a Path in a CDMA system requires movement of anat least 1 Chip in order to estimate the speed as same as (2), so thatit is not possible to detect the speed for a movement of a terminal thatis shorter than the length of 1 Chip.

[0010] (4) According to a conventional art to estimate a speed from thedisplacement of a career frequency by detecting a Path in a CDMA system,generally, the number of Paths is small, namely, 2 to 6 (in W-CDMA), sothat the accuracy of the estimation of the speed is low.

[0011] The present invention has been made taking the problems intoconsideration, an object of which is to provide a mobile radio terminalcapable of detecting a moving speed of the mobile radio terminal with atime and a moving distance which are shorter compared to a conventionalmethod and its moving speed detecting method.

BRIEF SUMMARY OF THE INVENTION

[0012] To achieve the above objects, in a first aspect, the presentinvention provides a moving speed detecting method of a mobile radioterminal which makes communication with a base station broadcasting apilot signal, comprising the steps of:

[0013] receiving the pilot signal at a first time;

[0014] predicting a first prediction characteristic value of a signal tobe received at a second time based on the received pilot signal by usinga first prediction method;

[0015] predicting a second prediction characteristic value of a signalto be received at the second time based on the received pilot signal byusing a second prediction method;

[0016] receiving a pilot signal at the second time after receiving thepilot signal at the first time;

[0017] generating an actual value of the pilot signal received at thesecond time;

[0018] calculating a first difference by comparing the predicted firstprediction characteristic value with the generated actual value;

[0019] calculating a second difference by comparing the predicted secondprediction characteristic value with the generated actual value;

[0020] detecting moving speed of the mobile radio terminal apparatusbased on the calculated first and second differences.

[0021] In a second aspect, the present invention provides a moving speeddetecting method of a mobile radio terminal which makes communicationwith a base station broadcasting a pilot signal, comprising the stepsof:

[0022] predicting phases and amplitudes of the pilot signal from thebase station by using a plurality of prediction methods having differentcharacteristics;

[0023] calculating errors for the prediction results, which are obtainedfor respective prediction methods in said prediction step; and

[0024] comparing the prediction errors with respect to each of theprediction methods, which are calculated by said calculating step, todetect a moving speed of said mobile radio terminal.

[0025] In a third aspect, the present invention provides a mobile radioterminal which makes communication with a base station broadcasting apilot signal, comprising:

[0026] first receiving means for receiving the pilot signal at a firsttime;

[0027] predicting means for predicting a first prediction characteristicvalue of a signal to be received at a second time based on the receivedpilot signal by using a first prediction method, and for predicting asecond prediction characteristic value of a signal to be received at thesecond time based on the received pilot signal by using a secondprediction method;

[0028] second receiving means for receiving a pilot signal at the secondtime after receiving the pilot signal at the first time;

[0029] generating means for generating an actual value of the pilotsignal received at the second time;

[0030] calculating means for calculating a first difference by comparingthe predicted first prediction characteristic value with the generatedactual value and for calculating a second difference by comparing thepredicted second prediction characteristic value with the generatedactual value;

[0031] detecting means for detecting moving speed of the mobile radioterminal apparatus based on the calculated first and second differences.

[0032] In a fourth aspect, the present invention provides mobile radioterminal which makes communication with a base station broadcasting apilot signal, comprising:

[0033] a predicting unit to predict phases and amplitudes of the pilotsignal from the base station by using a plurality of prediction methodshaving different characteristics;

[0034] a calculating unit to calculate errors for the prediction resultswhich are obtained for respective prediction methods by said predictingunit; and

[0035] a prediction error comparing unit to compare the predictionerrors with respect to each of the prediction methods, which arecalculated by said calculating unit, to detect a moving speed of saidmobile radio terminal.

[0036] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0037] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention, and together with the general description given above and thedetailed description of the embodiments given below, serve to explainthe principles of the invention.

[0038]FIG. 1 is a diagram for illustrating a constitution of a firstembodiment according to the present invention;

[0039]FIG. 2 is diagram for illustrating a specific constitution toestimate a moving speed of a mobile radio terminal 200;

[0040]FIG. 3 is a diagram for illustrating a constitution of aprediction method 2;

[0041]FIG. 4 is a diagram for illustrating tracks of separate pilotsignals on a complex plane by a solid line and a broken line;

[0042]FIG. 5 is a diagram for illustrating an amplitude variation of thesame fading by dB display;

[0043]FIG. 6 is a diagram such that a prediction error according to aprediction method 1 is obtained by a simulation when a radio frequencyand a slot frequency or the like are defined as a parameter of 1MT-2000of 3GPP; and

[0044]FIG. 7 is a diagram for illustrating a table including 73 piecesof coefficients to be used in the present embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0045] The embodiment of the present invention will be described indetail with reference to the drawings below.

[0046] (First Embodiment)

[0047]FIG. 1 shows a constitution of the first embodiment according tothe present invention. A left side of FIG. 1 comprises a base station100 and a right side thereof comprises a mobile radio terminal 200. Thebase station 100 includes a pair of transmission/reception antennas 101a and 101 b, a radio reception circuit 112, radio reception circuits 102a and 102 b, counting circuits 103 a and 103 b, a switch 104 and adecoder 113.

[0048] Alternatively, the mobile radio terminal 200 includes an antenna1, a radio reception circuit 2, despreading circuits 3 a, 3 b and 3 c,prediction circuits 4 a 1, 4 a 2, 4 b 1 and 4 b 2, a prediction errorcomparing circuit 5, selection circuits 6 a and 6 b, an encoder 7 and aradio transmission circuit 8. According to the first embodiment, theoutput of the prediction circuits 4 a 1 and 4 a 2 is only connected tothe prediction error comparing circuit 5.

[0049] The operation of the first embodiment will be explained below. Inthis explanation, an IMT-2000 mobile communication system defined by3GPP is taken as an example for a parameter with regard to transmission.According to a typical parameter, a radio frequency is 2 GHz band, atime interval to control a transmission antenna is about 667 μsecondsequivalent to 1.5 KHz and the number of antennas of the base station andthe number of pilot signals which are peculiar to the antenna is 2. Thepilot signals are orthogonal each other in code.

[0050] In FIG. 1, a unique pilot signal is steadily broadcast from twotransmission/reception antennas 101 a and 101 b of the base station 100.The information broadcast from the base station 100 to the mobile radioterminal 200 is spreaded by means which is not illustrated in thedrawings so as to be transmitted from any one of twotransmission/reception antennas 101 a and 101 b. It is decided dependingon the information from the mobile radio terminal 200 from which antennathe information is transmitted.

[0051] Alternatively, the IMT-2000 system controls the weight of asignal (a quantity of the information) to be transmitted from each ofthe two transmission/reception antennas 101 a and 101 b including aphase. However, in this case, in order to simplify the explanation, itis assumed that the IMT-2000 system comprises such a system as todetermine a transmission antenna alternatively (the weight of theantenna is 0 or 1 complementarily).

[0052] Each of the two transmission/reception antennas 101 a and 101 btransmits a signal including an at least specific pilot signal. Thesignals from the two transmission/reception antennas 101 a and 101 breach to the antenna 1 of the mobile radio terminal 200 via separatetransmission paths. Each of transmission paths includes scattering bythe object around the mobile radio terminal 200, so that so calledrayleigh fading is generated in accordance with the movement of themobile radio terminal 200. The mobile radio terminal 200 is capable ofseparately detecting amplitude and a phase of two pilot signals by twodespreading circuits 3 a and 3 b.

[0053]FIG. 4 shows tracks of separate pilot signals on a complex planeby a solid line and a broken line. FIG. 5 shows an amplitude variationof the same fading by dB indication. The mobile radio terminal 200observes the transmission loss from the two base station antennas 101 aand 101 b as described above. Then, as a result, it is detected fromwhich antenna the information component should be transmitted to receivethe information component at a higher level.

[0054] This detection result is encoded by an encoder 7 as atransmission antenna selection command and then, the encoded result istransmitted via a transmitter 8 and the antenna 1. The base station 100receives the transmitted result by a receiver 112 via the antennas 101 aand 101 b and a decoder 113 extracts a transmission antenna selectioncommand from the received result so as to control a transmission antennachanging switch 104. A principle of a feed back type transmissiondiversity is as described above.

[0055] According to the above explanation of the principle, the mobileradio terminal 200 observes the transmission loss of the twotransmission paths and the transmission antenna selection command istransmitted in units of a slot (1,500 Hz, 667 μseconds). Alternatively,the base station 100 receives the transmission antenna selection commandand switches one of antenna to another antenna to transmit theinformation component in accordance with this command also in units of aslot.

[0056] Further, there is a time delay for signal processing duringswitching the antenna, so that, in the case that the mobile radioterminal 200 observes the transmission loss in the (N)th slot, thisresult is reflected in a head of the (N+2)th slot. In other words, themobile radio terminal 200 predicts the transmission loss in the (N+2)thslot on the basis of the observation in the (N)th slot, so that themobile radio terminal 200 generates the transmission antenna selectioncommand.

[0057] As a method to predict the transmission loss, a method has beenconventionally known such that an observation value in the (N)th slot isdefined as a prediction characteristic value of the transmission loss inthe (N+2)th slot (a prediction method 1). This method is effective whenthe moving speed of the mobile radio terminal 200 is low. However, asthe moving speed becomes higher, the prediction accuracy isdeteriorated, so that the prediction errors are increased. If theprediction error according to the prediction method 1 is obtained by asimulation in the case that a radio frequency and a slot period or thelike are defined as a parameter of IMT-2000 of 3GPP, a property shown inFIG. 6 by a narrow line is obtained. As obvious from the drawing, theprediction error is not so large, i.e., −12 dB at 2 m per second.However, the prediction error is deteriorated at 18 m per second, i.e.,−6 dB.

[0058] On the other hand, as a prediction method 2, a method issuggested such that it predicts the transmission loss by the predictioncircuit configured by a FIR filter of a high order more than 30 stagesas shown in FIG. 3. In FIG. 3, reference numerals 41-1, 41-2, 41-3, . .. , and 41-72 denote holding circuits (1) to (72) for holding theinputted measured values. Further, reference numerals 42-1, 42-2, 42-3,. . . and 42-73 denote multiplication circuits to multiply the measuredvalue by a constant number. A counting circuit 43 adds the output fromthe above described multiplication circuits 42-1, 42-4, 42-3, . . . and42-73 and outputs the sum as the prediction value.

[0059]FIG. 3 shows an example of a FIR filter having 73 stages. If theprediction error is obtained by a simulation in the case of using 73pieces of the coefficients shown in FIG. 7 corresponding to this, aproperty shown by a bold line shown in FIG. 6 is obtained. As obviousfrom the drawing, the prediction error in the range of 2 m per second to18 m per second is constantly about −9 dB.

[0060] If the prediction error is compared to the observation valueafter time passes from the prediction, it is possible to know how thatprediction is precise. Alternatively, comparing respective predictionerrors of the above described two prediction methods in which relationsbetween the moving speed and the prediction errors are different, it ispossible to predict the moving speed of the mobile radio terminal 200.

[0061]FIG. 2 shows a specific constitution to estimate the moving speedof the mobile radio terminal 200. In FIG. 2, the prediction errorcomparing circuit 5 is configured by delay circuits 51 a and 51 b, errorgeneration circuits 52 a and 52 b, averaging circuits 53 a and 53 b anda comparing table 54. In FIG. 2, a reference numeral 1 denotes anantenna, a reference numeral 2 denotes a radio reception circuit, areference numeral 3 a denotes a despreading circuit and a referencenumeral 50 denotes a sampling circuit.

[0062] In the prediction error comparing circuit 5, the predictioncharacteristic value in the (N+2)th slot which is obtained by each thetwo prediction methods at the (N)th slot is delayed for two slots by thedelay circuits 51 a and 51 b. Then, the delayed prediction value iscompared to the observation value which is obtained at the (N+2)th slotin the error generation circuits 52 a and 52 b, so that the predictionerror is generated.

[0063] The prediction errors predicted by respective prediction methodsare compared to each other by the comparing table 54 after removing theinfluences such as a noise or the like therefrom by the averagingcircuits 53 a and 53 b. For example, according to the above describedexample, the comparing table 54 stores the data such that it outputs theestimation speed 2 m per second if the error predicted by the predictionmethod 1 is −12 dB and the error predicted by the prediction method 2 is−9 dB and it outputs the estimation speed 18 m per second if the errorpredicted by the prediction method 1 is −6 dB and the error predicted bythe prediction method 2 is −9 dB.

[0064] The methods to estimate the moving speed of the mobile radioterminal 200 are as described above.

[0065] (Modified Embodiment of the First Embodiment)

[0066] According to the above described first embodiment, the predictederrors are compared with respect to only one pilot signal. However,comparing the predicted errors with respect to other pilot signal, it ispossible to improve the accuracy in the estimation of the speed withputting together the results.

[0067] Alternatively, a parameter such as the number of the FIR stagesin the prediction method 2 shown in the above described first embodimentand the coefficients shown in FIG. 7 are taken as only an example. Ifthe number of the FIR stages is defined not less than about 30 stages,it is possible to obtain an effect by carrying out the presentinvention.

[0068] Alternatively, according to the above described first embodiment,the IMT-2000 system of 3GPP is taken as an example. However, it ispossible to carry out the present invention despite that thetransmission diversity is performed or not and without limiting thecommunication system to code division multiple access (CDMA). It is notpossible to apply the present invention to a system, which employs ananalog modulation system such as AMPS or the like. However, most of themobile radio communication systems, which employ a digital communicationsystem, include a signal referred to as a pilot signal and a uniqueword, so that, if the present invention is performed with respect tothis signal, as shown in the above described embodiment, the fading ispredicted by the different prediction methods and it is possible thatthe mobile speed is estimated from these prediction accuracy.

[0069] Alternatively, it is desirable that a content of the comparingtable 54, which is employed in the above described embodiment, ischanged by an electric power ratio of a desired signal and a noise(C/N). Therefore, it is possible to improve the accuracy of theestimation of the speed by modifying the comparing table and using atable to also input the C/N ratio.

[0070] According to the present invention, it is possible to estimatethe moving speed of the mobile radio terminal by a short measurementdistance, during a short measurement time and further, with a higherdegree of accuracy.

[0071] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A moving speed detecting method of a mobile radioterminal which makes communication with a base station broadcasting apilot signal, comprising the steps of: receiving the pilot signal at afirst time; predicting a first prediction characteristic value of asignal to be received at a second time based on the received pilotsignal by using a first prediction method; predicting a secondprediction characteristic value of a signal to be received at the secondtime based on the received pilot signal by using a second predictionmethod; receiving a pilot signal at the second time after receiving thepilot signal at the first time; generating an actual value of the pilotsignal received at the second time; calculating a first difference bycomparing the predicted first prediction characteristic value with thegenerated actual value; calculating a second difference by comparing thepredicted second prediction characteristic value with the generatedactual value; detecting moving speed of the mobile radio terminalapparatus based on the calculated first and second differences.
 2. Amoving speed detecting method of a mobile radio terminal according toclaim 1, wherein each of the steps of predicting the first and secondprediction characteristic values includes a step of predicting a phaseand an amplitude of the pilot signal, and the information with regard tothe phase and the amplitude of the pilot signal is commonly used as feedback information of a feedback type transmission diversity.
 3. A movingspeed detecting method of a mobile radio terminal according to claim 1,wherein one of said plurality of prediction methods comprises a methodsuch that a sampled pilot signal is defined as a prediction value of anext pilot signal as it is.
 4. A moving speed detecting method of amobile radio terminal according to claim 1, wherein a CN ratio of theobserved pilot signal is used as a parameter in the steps of calculatingthe first and second differences.
 5. A moving speed detecting method ofa mobile radio terminal which makes communication with a base stationbroadcasting a pilot signal, comprising the steps of: predicting phasesand amplitudes of the pilot signal from the base station by using aplurality of prediction methods having different characteristics;calculating errors for the prediction results, which are obtained forrespective prediction methods in said prediction step; and comparing theprediction errors with respect to each of the prediction methods, whichare calculated by said calculating step, to detect a moving speed ofsaid mobile radio terminal.
 6. A moving speed detecting method of amobile radio terminal according to claim 1, wherein the information withregard to the phase and the amplitude of the pilot signal, which arepredicted by said prediction step, is commonly used as feed backinformation of a feedback type transmission diversity.
 7. A moving speeddetecting method of a mobile radio terminal according to claim 1,wherein one of said plurality of prediction methods comprises a methodsuch that a sampled pilot signal is defined as a prediction value of anext pilot signal as it is.
 8. A mobile radio terminal which makescommunication with a base station broadcasting a pilot signal,comprising: first receiving means for receiving the pilot signal at afirst time; predicting means for predicting a first predictioncharacteristic value of a signal to be received at a second time basedon the received pilot signal by using a first prediction method, and forpredicting a second prediction characteristic value of a signal to bereceived at the second time based on the received pilot signal by usinga second prediction method; second receiving means for receiving a pilotsignal at the second time after receiving the pilot signal at the firsttime; generating means for generating an actual value of the pilotsignal received at the second time; calculating means for calculating afirst difference by comparing the predicted first predictioncharacteristic value with the generated actual value and for calculatinga second difference by comparing the predicted second predictioncharacteristic value with the generated actual value; detecting meansfor detecting moving speed of the mobile radio terminal apparatus basedon the calculated first and second differences.
 9. A mobile radioterminal according to claim 8, wherein the predicting means includesmeans for predicting a phase and an amplitude of the pilot signal,wherein the information with regard to the phase and the amplitude ofthe pilot signal, which are predicted by said predicting unit, iscommonly used as the feed back information of a feedback typetransmission diversity.
 10. A mobile radio terminal according to claim8, wherein one of said plurality of prediction methods comprises amethod such that a sampled pilot signal is defined as a prediction valueof a next pilot signal as it is.
 11. A mobile radio terminal accordingto claim 8, wherein a CN ratio of the observed pilot signal is used as aparameter in calculating the first and second differences by saidcalculating means.
 12. A mobile radio terminal which makes communicationwith a base station broadcasting a pilot signal, comprising: apredicting unit to predict phases and amplitudes of the pilot signalfrom the base station by using a plurality of prediction methods havingdifferent characteristics; a calculating unit to calculate errors forthe prediction results which are obtained for respective predictionmethods by said predicting unit; and a prediction error comparing unitto compare the prediction errors with respect to each of the predictionmethods, which are calculated by said calculating unit, to detect amoving speed of said mobile radio terminal.
 13. A mobile radio terminalaccording to claim 12, wherein the information with regard to the phaseand the amplitude of the pilot signal, which are predicted by saidpredicting unit, is commonly used as the feed back information of afeedback type transmission diversity.
 14. A mobile radio terminalaccording to claim 12, wherein one of said plurality of predictionmethods comprises a method such that a sampled pilot signal is definedas a prediction value of a next pilot signal as it is.
 15. A mobileradio terminal according to claim 12, wherein a CN ratio of the observedpilot signal is used as a parameter upon comparing the prediction errorin a plurality of prediction methods having different characteristics insaid prediction error comparing unit.